Super-power (e.g. 200 megawatts peak) klystrons operating with high voltage (e.g. 600 kV) linear electron beams are employed for various purposes, for example, as excitation sources for linear accelerators and output tubes for high power transmitters. Such klystrons require electrons having velocities in the relativistic regime.
Prior art super-power klystrons typically include an output resonant cavity structure operating in the TM.sub.010 mode and include re-entrant drift-tubes forming interaction gaps for strong coupling to an electron beam propagating in the tube. High electric fields at metal boundaries of the interaction gap are susceptible of producing arcing. The RF voltage which can be established across the interaction gaps is thereby limited by the arcing effects. To increase the overall voltage established across the output resonant cavity structure, such structure usually includes several resonators electrically coupled together by magnetic coupling slots; such a structure is often referred to as extended interaction resonators. The extent to which the several resonators can be coupled together to increase the resonator voltage to provide the required performance in a satisfactory manner depends on internal coupling required for adequate power flow to maintain a uniform voltage distribution among the individual gaps. The success of this structure also depends on the proximity of neighboring resonant modes that affect the tube bandwidth requirements.
The prior art structures require relatively large electron beam tunnel diameters to provide the beam optics necessary for proper klystron operation, i.e. the tunnel diameter is a relatively large percentage of the diameter of the side walls of the extended interaction resonators. The large tunnel diameter is a complication in high voltage super-power klystron tubes because it increases the amount of direct electric coupling between the interaction gaps and opposes magnetic coupling through the coupling slots. Recent analysis indicates it is extremely difficult, if not impossible, to provide a super-power klystron output resonator if conventional design approaches are employed.
It is, accordingly, an object of the present invention to provide a new and improved cavity resonator particularly adapted for use as an output resonator structure in super-power klystrons.
It is another object of the invention to provide a new and improved super-power klystron operating with high-beam voltage to produce electron velocities in the relativistic regime, wherein said klystron includes a new and improved output resonator structure.
Another object of the invention is to provide a new and improved super-power, high voltage klystron having an output resonator with a relatively small peripheral volume and a low level electric field on surfaces of the resonator.
An additional object of the invention is to provide a new and improved super-power, high voltage klystron having an output cavity with a characteristic impedance compatible with the low beam impedance of such klystrons.
A further object of the invention is to provide a new and improved super-power, high voltage klystron with an output cavity having a relatively short length for the tube operating frequency.
A further object of the invention is to provide a new and improved super-power, high voltage klystron wherein the spacing between electric field peaks in the klystron resonant cavity output structure is maintained, to provide good interaction with the klystron electron beam.